1. Field of the Invention
The present invention relates generally to hydraulic fracturing of oil wells, and particularly to a method for aligning perforations with the direction of hydraulic fracture propagation from the well bore that is generally in a direction perpendicular to the least principle horizontal stress.
2. Prior Art
In many instances, after a well is drilled to a desired depth, fractures must be induced in the surrounding formation in order to produce commercially significant quantities of hydrocarbons from the well. Prior art techniques of fracturing a well generally involve the use of multiple charge perforating guns that are used to perforate the formation in multiple locations for a given length of the well. Such perforations could be made in either a random or organized pattern.
Thereafter, through techniques commonly employed in the industry, fractures in the formation would be induced by pumping a fracturing fluid, containing proppants, under high pressure, into the well bore and through certain of the perforations until a fracture was initiated. Fracturing operations were then continued until the fractures were propagated a sufficient distance into the formation surrounding the well bore.
It is well known that after initiation of a fracture, a fracture will propagate away from the well bore in a radial direction that is perpendicular the minimum principle stress existing in the surrounding formation, i.e., the direction of propagation of the fractures is controlled by the state of stress existing in the surrounding formation. Nevertheless, heretofore, there has been no attempt in the art to align the perforations produced by the perforating guns with the direction of fracture propagation, i.e., perpendicular to the minimum principle horizontal stress existing within the formation.
Certain problems encountered in fracturing operations are believed to have been due to the failure of prior art methods and techniques to align the perforations with the direction of fracture propagation within a formation. In particular, nonalignment of the perforations resulted in the use of excessive pressures to fracture the well, and resulted in the development of a tortuous flow path for the fracturing fluid as it flowed from the initial fracture formed in a nonaligned perforation tunnel to the main fracture. The tortuous path developed because a fracture that was initiated at a non-aligned perforation tunnel would curve as it propagated through the formation to align itself with the direction of propagation of the main fracture. This tortuous path caused excessive pressure drop as the fracturing fluid was pumped therethrough, and generally inhibited the timely and efficient completion of a well such that maximum production could be achieved therefrom.
The present invention solves all of the aforementioned problems by insuring alignment of the perforations with the direction of fracture propagation within a field. By employing the method disclosed and claimed herein, lower fracture initiation pressures may be obtained, and other problems associated with near well bore tortuosity may be overcome.